Agent skill
processing-parallel-tasks
Implements parallel processing using Parallel, PLINQ, and ConcurrentCollections in .NET. Use when processing CPU-bound tasks in parallel or improving multi-core utilization.
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SKILL.md
.NET Parallel Processing
A guide for APIs and patterns for parallel processing of CPU-bound tasks.
Quick Reference: See QUICKREF.md for essential patterns at a glance.
1. Core APIs
| API | Purpose |
|---|---|
Parallel.For, Parallel.ForEach |
CPU-bound parallel processing |
PLINQ (.AsParallel()) |
LINQ query parallelization |
Partitioner<T> |
Large data partitioning |
ConcurrentDictionary<K,V> |
Thread-safe dictionary |
2. Parallel Class
2.1 Parallel.ForEach
csharp
public sealed class ImageProcessor
{
public void ProcessImages(IEnumerable<string> imagePaths)
{
var options = new ParallelOptions
{
MaxDegreeOfParallelism = Environment.ProcessorCount
};
Parallel.ForEach(imagePaths, options, path =>
{
ProcessImage(path);
});
}
}
2.2 Early Termination
csharp
Parallel.For(0, data.Length, (i, state) =>
{
if (data[i] == target)
{
state.Break();
}
});
3. PLINQ
csharp
var results = data
.AsParallel()
.WithDegreeOfParallelism(Environment.ProcessorCount)
.Where(d => d.IsValid)
.Select(d => Transform(d))
.ToList();
// When order preservation is needed
var results = data
.AsParallel()
.AsOrdered()
.Select(d => Process(d))
.ToList();
4. Thread-Safe Collections
| Collection | Purpose |
|---|---|
ConcurrentDictionary<K,V> |
Thread-safe dictionary |
ConcurrentQueue<T> |
Thread-safe FIFO queue |
ConcurrentBag<T> |
Thread-safe unordered collection |
csharp
// Collecting results during parallel processing
var results = new ConcurrentBag<Result>();
Parallel.ForEach(data, item =>
{
var result = Process(item);
results.Add(result);
});
5. ThreadLocal<T>
Prevents contention with thread-local variables
csharp
private readonly ThreadLocal<StringBuilder> _localBuilder =
new(() => new StringBuilder());
public void ProcessInParallel()
{
Parallel.For(0, 1000, i =>
{
var sb = _localBuilder.Value!;
sb.Clear();
sb.Append(i);
});
}
6. Important Notes
Parallel Processing vs Async
- CPU-bound: Use Parallel
- I/O-bound: Use async-await
csharp
// ❌ Using Parallel for I/O operations
Parallel.ForEach(urls, url => httpClient.GetAsync(url).Result);
// ✅ Using async-await for I/O operations
await Task.WhenAll(urls.Select(url => httpClient.GetAsync(url)));
Shared State Synchronization
csharp
// ❌ Parallel writes to regular collection
var list = new List<int>();
Parallel.For(0, 1000, i => list.Add(i)); // Race condition!
// ✅ Using thread-safe collection
var bag = new ConcurrentBag<int>();
Parallel.For(0, 1000, i => bag.Add(i));
7. References
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